Acoustical material and method of making the same



INVENTOR 2 Sheets-Sheet 2 L. W. ECKERT Jan. 23, 1962 ACOUSTICAL MATERIAL AND METHOD OF MAKING THE SAME Filed June 18, 1957 LEWIS W. ECKERT l ATTORNEY United States Patent Office 3,017,947 Patented Jan. 23, 1962 3,017,947 ACUSTECAL MATERAL AND METHD F MAKING THE SAME `Lewis W. Eckert, Lancaster Township, Lancaster County, lPa., assigner to Armstrong Cork Company, Lancaster, Pa., a corporation of Pennsylvania Filed June 18, 1957, Ser. No. 666,4fi7 2 Ciaims. (Cl. 181-33) This invention relates to an acoustical material and ymethod of making the same, and more particularly to a method in which the base material is dried, after which the surface is ruptured to form irregularly shaped elongated sound-absorbing openings to expose the interstices existing between the fibers in the body of the material.

Improvements in the sound-absorbent characteristics have been imparted to fibrous sheet material through two primary methods. The one method is the drilling of holes from the face through substantially the entire depth of the material, and the second method is the reorientation of the fibers of which the material is composed to form openings in the surface leading to fissures between the fibers. The purpose of these methods is to expose'the fibrous structure of the interior of the board for entrapping sound and thereby giving the room in which the material is installed the desired acoustical treatment. The fissuring method has been limited to certain types of materials composed of relatively short fibers which are not intertwined to any great extent.

Typical of the acoustical materials which can be fissured during the wet forming process are the ones made from a slurry of mineral wool and/or glass wool and the like, in which lthe fibers are present in clumps and are coated with a starch binder.- When this newly formed slurry is screeded or subjected to controlled pressure by a fissuring roll, as shown in United States Patent No. 2,717,538, the clumps are reoriented to such an extent that the laminae of clumps forming the face layer are tilted so as to form a surface on the slurry which is discontinuous by reason of the fact that short sections thereof are disposed at a slight angle with respect to the longitudinal plane of the slurry, exposing crevices or fissures between adjacent areas of disrupted surface. Inasmuch as the starch binder has not set when the surface of the slurry is subjected to this fissuring operation, the individual fibers in the clumps are free to reorient themselves with respect to the other fibers and the clumps are free to reorient themselves with respect to the other clumps. When the water of formation is removed from the fibrous mass and the binder sets, the surface maintains a tilted appearance with the fissures disposed therebetween. When the rough surface is removed by a sanding or grinding operation, the face of the sheet is discontinuous with fissures disposed haphazardly thereover.

In this type of material, which can be wet fissured, the uncontrolled location of the fissures is not desirable, because in cutting the dried mat into 12x 12" tiles or any other desired size, it is difiicult to obtain tiles with the same over-all degree of fissuring. Then, too, with this type of fissure it is ofttimes necessary in cutting the tile from the sheet to cut through a fissure which weakens the edge of the tile, making it unsuitable for use.

Another type of acoustical material currently sold in large volumes is that formed from a water-laid mat of vegetable fibers similar to conventional insulating board. In this type product, in order to attain the necessary strength and still keep the binder content low enough to provide sufficient interstices between the intertwined fibers, it is essential that the fiber length be carefully controlled. If the percentage of short fibers is too great, the sheet is too dense and will not be suitable as a sound-absorbing material. lIt has been found in making a vegetable fiberboard suitable for sound-absorption purposes that it is desirable to have a fibrous system having approximately 10% to 12% fibers which are retained on a 10- mesh screen; 16% retained on a 20 mesh screen; 16% retained on a 35 mesh screen; 18% retained on a 65 mesh screen; and the balance of fibers which will pass through a 65 mesh screen. In this structure, the shorter fibers serve as binders to secure the large fibers to one another at their points of contact with one another. The fine fibers migrate to the surface during the wet forming operation and form the smooth outer face of the material back of which is the rigid structure formed of the long fibers bound together by the short fibers forming interstices which do not communicate with the surface of the sheet. With this interlace system, it is impossible to reorient the fibers to form fissures extending from the surface into the interior of the sheet by screeding or by the application of pressure to the surface by means of a roller, as in the case of the mineral fiber discussed above.

Because of the lack of practical means for simulating fissures in vegetable fiberboard, most acoustical material made from this product is limited to that having drilled holes to admit sound to the interior interstices.

This invention has been developed to provide a means whereby the conventional fiberboard type acoustical materials, as well as the previously dried mineral wool and glass wool materials, can be treated to give the same appearance as the mineral wool fibrous materials which have been wet fissured.

The method here under consideration is directed to a punching operation in which a heavy plate is pressed into the surface of the dry fibrous sheet. This plate has in relief thereon the design of the irregularly shaped elongated openings desired for the finished acoustica1 material. This plate may be made of any of the conventional alloys suitable for withstanding the stress and wear resulting from the high speed operation, and the projections which are forced into the fiberboard have rather rough jagged edges so as to prevent the actual cutting of the fibers in the board but instead merely push a portion of the surface of the sheet into the sheet, leaving exposed edges along the openings as the plate projections enter the material to form sound-absorbing openings in the material. These openings, while devoid of fibers themselves, are lined with loosely entwined fibers which absorb and entrap sound. The projection entering the material does not actually cut the surface but tears a portion from the surface and pushes it into the body of the material.

An object of this invention is to provide a fiberboard acoustical material of the vegetable fiber type which has irregularly shaped elongated openings therein similar in appearance to the wet formed fissures in some of the acoustical materials made from mineral fibers.

Another object of this invention is to provide a method whereby fibrous acoustical material may be treated after it has been formed from a water-laid mass of fibrous material and dried to present irregularly shaped elongated openings on the surface.

A still further object of this invention is to provide a method whereby the surface of fiberboard may be disrupted by placing irregularly shaped elongated openings therein without changing the dimensional stability of the fiberboard.

A still further object of this invention is to provide a method whereby the portion of material at the bottom of the irregularly shaped elongated opening is of a darker shade so that the opening will be more pronounced.

In order that the invention may be more readily understood, it will be described in connection with the attached drawing, in which:

FIGURE 1 shows a face view of the sound-absorbing surface of the fiberboard of this invention;

FIGURE 2 shows a back view of the fiber-board;

FIGURE 3 is a diagrammatic view of the forming, drying and dyeing process;

FIGURE 4 is a continuation of the right-hand end of FIGURE 3, showing a side elevational view of the equipment used for placing the sound-absorbing openings in the face of the tile and the embossed pattern on the back of the tile; and

FIGURE 5 is an enlarged cross-sectional view of the tile produced by the method, taken on line 5-5 of FIG. l.

In carrying out the invention, the fiberboard sheet material 2 (FIG. 3) is produced in the conventional manner on a Wet forming board machine I8 such as that shown in U.S. Patent No. 1,927,360 and dr-ied to the desired degree in a conventional drier 19 such as shown in US. Patent No. 1,990,554. During the formation of the board, a dark dye is doctored on the surface of the board at the wet end by means of a doctoring device 20 such as that shown in U.S. Patent No. 1,944,528. In this dye-applying device, the dye is applied from a tube ZI to the surface of the board 2. The doctor blade 22 carried by the support 23 levels the dye into a smooth, uniform coat on the surface 10 of the board. The purpose of' this dye will be explained later. The blanks are then fed over conventional rollers 2,4 to a suitable punch press 3 (FIG. 4). These blanks are usually of a 4' x 8 size, and the punch press 3 which places irregularly shaped elongated openings 4 in the material is provided with a plate S which is 4 x l. In the preferred embodiment, this is made up of a plurality of square plates l x l". The board 2 is fed intermittently through the press 3, with each stroke of the press placing openings in a new area of the blank. Y

In order to increase the sound absorption of the materi'al, small holes 6 may be punched inthe intermediate areas between the irregularly shaped elongated openings 4; and if fine punches are used, the holes will not be obvious to 'the eye of a casual observer, but nevertheless a great amount of sound will be absorbed by the small punched holes, increasing the accessibility to the interior, thus greatly increasing the eli'lciency of the acoustical material.

These small pins can be on the same plate as the irregularly shaped elongated projections if desired, but the preferred arrangement of the pins is to form a separate plate 7 positioned in the punch press 3, adjacent the plate S having the irregularly shaped projections. With this arrangement, on each stroke of the press a 4 x l section of the sheet 2 will be subjected to the irregularly shaped projections 8 and the adjacent 4 x l section will be subjected to the pins 9. inasmuch as the board 2 moves only the width of one plate on each stroke of the press, one section is completed in each stroke of the press and the adjacent section is half completed. This, of course, does not hold true for the first stroke of the press at the start of a sheet; however, after the press is started, the sheets are fed in abutting relationship.

In designing the plate 7 with the pins 9 for punching the small holes 6, it should be so arranged that the pins 9 engage the material in the areas which are not engaged by the plate forming the irregularly shaped elongated openings 4. This increases the sound-absorption qualities of the material. Also, both the plate having the elongated projections 8 and the plate having the pins 9 should be so .arranged that neither the irregularly shaped elongated openings 4 nor the punched holes 6 will occur close to the edges of the cut tile, making it possible to produce tile having strong edges.

The pins 9 utilized in punching the holes 6 in the acoustical tile between 'the irregularly shaped elongated openings are preferably of a unique design to produce the desired amount of sound absorption and at the same time produce a clear-cut opening on the surface so as not to .be ,readily discernible on mere visual observation. In

order to insure these desired results, it has been found advantageous to use pins of a diameter of approximately .100 which have had the pointed tips ground down to a flat tip lapproximately .050" in diameter. This design of pins overcomes the objection to a pierced hole made by a sharp pointed instrument in that the instrument is forced into the material and the bers are merely pushed aside and upon Withdrawal of the pointed object the fibers tend to come together again and more or less heal the opening. This is particularly true of holes made by o-bjects of such small diameter. With a punch of the type here described, the blunt nose engages the surface of the material first, and as it enters the material it pushes and tears the iibers, disarranging the laminae of the iibers along the edges. The taper on the punch beyond the blunt end increases'the size of the hole, and in so doing takes care of any slight damage such as irregular tears which might occur on thesurface of the tile due to the blunt end of the punch entering the material. VThe hole resulting after the punch is withdrawn has a clean-cut appearance, while the sideof the hole has disarranged laminae of fibers, exposing the interstices of the material for sound-absorption purposes.

'I his punching operation on the dried board, of course, disrupts the liber orientation system on the one surface I0 of the board to a considerable extent and has the effect of stretching the one surface of the sheet but has no disrupting effect on the fiber orientation system on the other side Il of the sheet. This stretching and disrupting effect on the fibers on the surface l0 of the board relieves some of the stresses buil-t up in the fibers on that surface, While f the stress on fibers on the other surface 11 remains unchanged. This unbalanced condition causes the board to warp so that the finished l2" x 12" tile will be warped in such manner that it cannot be satisfactorily secured to the ceiling or other relatively flat surface.

In order to overcome this objection, it has been found that at the same time the irregularly shaped elongated openings are being pressed into the surface of the board, a uniform pattern of fiber disruption can be effected on the back 11 of the board which will relieve the stressed fibers in the back of the board to such an Vextent that it will stretch to the same proportion as the face 10 of the board, or to a proportion sufficiently similar to the stretching of the face so as to prevent warping of the finished tile. This can be accomplished satisfactorily by placing a bed plate IZ in the press 3 having a design thereon to be embedded in the back of the sheet at the same time that the punching operation is performed on the face of the material. For this purpose, it has been found satisfactory to utilize a design similar to that shown in FIGURE 2.

In the particular embodiment found preferable, the indentations I3 remaining on the tile are approximately W16 long x 1/16" wide, with 1/s" space therebetween, both lengthwise and sidewise These indented areas are depressed to a depth of approximately 1/32. It may be found that other designs of back ber disruption may be mo-re desirable `for other thicknesses or other 'fiber compositions.

After manufacture, the back of the tile may be sanded to remove the indentations I3 or they may be retained on the back of the tile.

The blank to be punched is positioned over the bed plate I2 having the desired design, and as the press 3 closes the plate 5 on the press forms the irregularly shaped elongated openings in the face 10 of the tile and presses the back 1I of the tile against the bed plate 12 to impart a design on the back similar to that shown in FIG- URE 2 of the drawing. The number of indentations 13 embossed on the back of the tile should be determined to a 'certain extent by the number of irregularly shaped elongated openings 4 placed in the face of the tile. For example, if a relatively small number of such openings are distributed evenly over the face of the sheet, then it will be necessary to have only a limited number of indentations 13 on the back of the sheet to compensate for the warpage; however, if a larger number of such openings are placed on the face of the sheet, then it may be found desirable to have a greater number of offsetting indentations 13 on the back of the sheet to compensate for the deformities caused by the openings.

When high-grade wood fibers are used in the manufacture of fiberboard, the board is rather light in color and there is no great contrast from the usual white or ivory paint applied to the surface `of the tile after the manufacturing operation has been completed. During the punching operation, a certain area of the surface of the tile is formed into the tile and forms the bottom of the irregularly shaped elongated opening 4. This is undesirable, because with this light-colored material in the bottom of the opening, the opening does not stand out to any appreciable extent. In order to overcome this difficulty, the surface of the sheet is treated with a dark dye prior to the punching step. This dark-colored material in the bottom of the opening contrasted with the light color on the surface of the material makes the opening stand out and lends a much greater decorative effect to the acoustical material. If desired, the dye may be included throughout the body of the material so that the interior of the irregularly shaped elongated openings will 4be darker than the paint applied to the surface. Also the dye can be applied to the surface of the tile after the punching operation and then wiped into the opening by a squeegee, thus coating the interior of the openings with the dye.

The plate 5 which is urged into engagement with the surface of the material to form the irregularly shaped elongated openings 4 is preferably made so that the projections are not sharp on their outer extremity but are blunt and will, therefore, have a punching and tearing effect rather than a cutting effect. An opening formed with this type of instrument will maintain its original configuration rather than close as will be the case of an opening which is merely cut in the material by a sharp instrument being thrust into it and withdrawn. This gives a better opening for sound absorption purposes than the type made from a sharp cutting instrument which merely severes the fibers and forms an opening in the surface of the material compacting the fibers along the edges thereof. The desired type of plate has a definite punching and tearing effect on the fberboard rather than a cutting effect. During this tearing and delaminating process, not all laminae 14 are torn on the same vertical plane; but as the projection continues into the material, it tears a larger area from each lamina 14 as it progresses resulting in an undercut effect 15 so that the inner opening 16 is really larger than it appears on the surface.

The material is painted after punching; however, if such painting is done by the roller applicator, it will be understood that the area 17 in the bottom of the opening will not be affected by the paint. It will be obvious to those skilled in the art that the article and method herein described can be carried out to form an acoustical material which will have the appearance of the more expensive wet ssured material and have the high coefficient of sound absorption of the conventional punched type sound absorption material. The method may be set up in production line technique and may be used for both vegetable fiber tiles and mineral ber tile.

I claim:

l. A method of producing sound absorbing material, the steps comprising forming a water-laid mat of fibrous material with suitable binder constituents, drying said mat to form a sheet of intertwined fibers having sound absorbing interstices throughout and having a relatively smooth impervious surface, coating one flat surface of said sheet with a dark dye, urging a plurality of irregularly shaped elongated projections into engagement with the dyed surface of said sheet to push certain areas of said surface into the body -of the sheet exposing sound absorbing interstices in the interior of the sheet and forming irregularly shaped elongated openings on the surface of said sheet, and simultaneous with the forcing of the irregularly shaped elongated projections into the surface of the sheet embossing a pattern on the back of said sheet.

2. A method of producing sound absorbing material, the steps comprising forming a water-laid mat of fibrous material with suitable binder constituents, drying said mat to form a sheet of intertwined fibers having sound absorbing interstices throughout and having a relatively smooth impervious surface, coating one fiat surface of said sheet with a dark dye, urging a plurality of irregularly shaped elongated projections into engagement with the dyed surface of said sheet to push certain areas of said surface into the body of the sheet, exposing the sound absorbing interstices in the interior of the sheet and forming irregularly shaped elongated openings on the surface of the sheet, and simultaneously therewith urging an embossing plate into engigement with the back of the sheet to emboss a grid design thereon.

References Cited in the ile of this patent UNITED STATES PATENTS 1,856,898 Wood May 3, 1932 1,875,074 Mason Aug. 30, 1932 2,008,278 Goss July 16, 1935 2,355,454 Lucius Aug. 8, 1944 2,572,470 Gordon Oct. 23, 19511 2,611,434 Mugler Sept. 23, 1952 2,667,925 Dalphone Feb. 2, 1954 2,668,123 Copeland Feb. 2, 1954 2,717,538 Alexander Sept. 13, 1955 2,791,289 Proudfoot May 7, 1957 2,874,796 Eckert Feb. 24, 1959 

1. A METHOD OF PRODUCING SOUND ABSORBING MATERIAL, THE STEPS COMPRISING FORMING A WATER-LAID MAT OF FIBROUS MATERIAL WITH SUITABLE BINDER CONSTITUENTS, DRYING SAID MAT TO FORM A SHEET OF INTERTWINED FIBERS HAVING SOUND ABSORBING INTERSTICES THROUGHOUT AND HAVING A RELATIVELY SMOOTH IMPERVIOUS SURFACE, COATING ONE FLAT SURFACE OF SAID SHEET WITH A DARK DYE, URGING A PLURALITY OF IRREGULARLY SHAPED ELONGATED PROJECTIONS INTO ENGAGEMENT WITH THE DYED SURFACE OF SAID SHEET TO PUSH CERTAIN AREAS OF SAID SURFACE INTO THE BODY OF THE SHEET EXPOSING SOUND ABSORBING INTERSTICES IN THE INTERIOR OF THE SHEET AND FORMING IRREGULARLY SHAPED ELONGATED OPENINGS ON THE SURFACE OF SAID SHEET, AND SIMULTANEOUS WITH THE FORCING OF THE IRREGULARLY SHAPED ELONGATED PROJECTIONS INTO THE SURFACE OF THE SHEET EMBOSSING A PATTERN ON THE BACK OF SAID SHEET. 